1. Field of the Invention
This invention relates to a method for formation of a functional film, particularly a functional deposited film which is useful for in semiconductor devices, photosensitive devices for electrophotography, electronic device such as optical input sensor devices for optical image inputting device, etc.
2. Related Background Art
In the prior art, for amorphous or polycrystalline functional films such as semiconductor films, insulating films, photoconductive films, magnetic films or metal films, individually suitable film-forming methods have been employed from the standpoint of desired physical characteristics, uses, etc.
For formation of deposited films, there have been attempted the vacuum vapor deposition method, the plasma CVD method, the thermal CVD method, the optical CVD method, the reactive sputtering method, the ion plating method, etc. Generally, the plasma CVD method has been widely used and industrialized.
However, the deposited films obtained according to these methods for formation of deposited films have been demanded to be used in electronic devices or photoelectronic devices for which higher functions are required, and therefore there is room for further improvement in their overall characteristics with respect to electrical and optical characteristics, and fatigue characteristic or environmental resistance characteristic on repeated use, and further productivity, bulk productivity, including uniformness, reproducibility, etc.
The reaction process in formation of a deposited film according to the plasma CVD method which has been generalized in the prior art is considerably more complicated than the thermal CVD method of the prior art, and its reaction mechanism involves several ambiguities. Also, there are a large number of parameters in the formation of a deposited film (for example, substrate temperature, flow rate and flow rate ratio of the introduced gases, pressure during formation, high frequency power, electrode structure, structure of the reaction vessel, speed of evacuation, plasma generating system, etc.). Because of the combination of such a large number of parameters, the plasma may sometimes become unstable, whereby significant deleterious influences are exerted frequently on the deposited film formed. Besides, the parameters characteristic of the device must be selected for each device and therefore under the present situation it has been difficult to generalize the production conditions.
Also, depending on the application use of the deposited film, bulk production having reproducibility must be obtained with full satisfaction of enlargement of area, uniformity of film thickness as well as uniformity of film quality, and therefore in formation of a deposited film according to the plasma CVD method, enormous installation investment is required for a bulk production device and also controls for such bulk production become complicated, with the management tolerance being narrow and the control of the device being severe. These are pointed out as the problems to be improved in the future.
Further, according to the the conventional prior art CVD method, high temperature is required and a deposited film having satisfactory characteristics on industrial level could not necessarily be obtained.
These remain as the more significant problems particularly in the case of forming a thin film of Group II-VI compounds.
As described above, in formation of functional films, it has been earnestly desired to develop a method for forming a deposited film which is capable of bulk production by means of a device of low cost, while maintaining the characteristics as well as uniformity which are practicably available.